A Vivaldi antenna element is a radiating element having a tapering slot or notch formed by the element which produces a linear polarisation to the radiated signal. An example of a Vivaldi antenna is described in patent application GB1601441.
Vivaldi type elements have been incorporated into larger arrays to form phased array antennas as described in EP0349069. The antenna produces radiated signals having planes of polarisation which are orthogonal and it is used in radar and other direction finding applications. The array is formed by horizontal and vertically disposed planar substrates bearing the metallised layers etched to produce the antenna elements. The substrates are configured to interlock by means of inter-engaging projections and rebates and the array is formed into a number of square sectioned open ended boxes with the sides of the boxes each bearing a tapering Vivaldi notch. The problem of coupling signals into and out of the notch when the two orthogonal notches have phase centres which are co-located is addressed in an imperfect manner in the prior art described in that document. Indeed the problem is described as insurmountable and another approach is adopted namely ensuring that phase centres of the elements are not co-located. However, by not co-locating the phase centres it is necessary for signal processing to be employed that compensates for the arrival of an incoming signal at phase centres at different times and this is undesirable.